Replacing Windows in Brick-Veneer Homes

Flashing is critical, but it's not always so easy to get to

I have replaced hundreds of windows in brick-veneer homes across
Long Island. The coastal environment requires a little extra care,
but the procedure is essentially the same for any climate. The
tricky part with brick is getting the flashing in the right
place.

With most window replacement jobs, the ideal installation requires
the removal of the siding, which allows the window to be integrated
with the existing weather-resistive barrier (WRB). In a
brick-veneer structure, however, that's not so easy. Removing aged
brick and mortar to access the window is certain to be noticed long
after the job is done. The additional cost associated with surgical
removal and the painstaking process of matching new brick and
mortar is often prohibitive to most clients. So I resort to the
methods described here. The procedures are a compromise, but
they're a lot better than leaving an old drafty, leaky
window.

Measurement Is Key

The selection of the proper window is the primary consideration in
this environment. I prefer to use a "prime" window. One I use a lot
is the Andersen replacement window; it can be custom sized to fit
the openings perfectly, which makes all the difference. But any
high-quality window with a nailing flange system will work if you
can get the right size for the existing openings.

Pay attention to measuring for the new window. When the window
opening is in place, the flange will be secured to the framed wall
and will be recessed into the brick opening. To ensure a watertight
installation, you need enough room to integrate the flashing with
the existing WRB.

There are two measurements of concern here: the rough opening (RO)
and the brick opening (BO). The RO is the interior dimension of the
framed wall opening. This is the opening we are most familiar with
when installing windows in a framed wall. The BO, on the exterior,
must be big enough to give us room to maneuver with our flashing
around the new window. This space will get covered with an exterior
brick mold once the new window is in place.

If we're lucky enough that the existing window has a wood-frame
window with a brick-mold exterior trim, the existing RO can usually
be used to order the new window. The old brick mold provides the
room we need to integrate the flashing. But most of the
applications I see involve old metal-frame windows (usually steel
or aluminum) that were mounted to the RO prior to the application
of the brick veneer. The edges of the window typically come right
to the edge of the BO, and the flanges are buried behind the brick.
Steel-frame double-hungs, which have a spring mechanism buried in
the jambs, have an even larger RO. In any of these cases, we can't
use the existing RO to order new windows.

The key to a flawless window replacement in a brick-veneer wall
is sizing the new window properly. The replacement unit must be
small enough to fit through the existing brick opening without
having to dismantle the brick and mortar, but large enough to
minimize the unsupported flashing and allow the new unit to be
inconspicuously trimmed out.

Instead, I first measure the BO from the exterior, then open the
window and reference the available RO to the BO. The window should
fit in the BO with enough room to allow at least 1 1/4 to 1 1/2
inches on both sides of the window (Figure 1) and a minimum of 3/4
inch on the top. It may be necessary to pack out the old RO to
create an opening that is this much smaller than the BO. Ideally, I
like to have 2 inches on the bottom, too, but I rarely get that and
will settle for less if necessary.

Figure 1. Minimum Opening Sizes

The window should be sized to fit in a rough opening (RO) in
the framed wall that's at least 11/4 to 11/2 inches smaller than
the brick opening (BO). Ideally, this BO would also be 2 inches
higher than the RO to allow room at the head and sill, but the
window can still be made to fit through a smaller BO if the bottom
flange is removed before it's installed.

Integrating New Flashing and the Existing
WRB

Almost every job I have done has had No. 30 felt or building paper
over the framed walls as a WRB. When removing the old window, care
must be taken to preserve the integrity of this existing WRB. After
a number of years it can become dry and brittle, so we have to be
gentle to keep from tearing it up when working the opening.

Once the old window is out, we focus our attention on preparing the
opening, using a metal sill pan and flexible flashing, as outlined
in Figure 2. It's important to use a sill pan that gives you an
upturned edge on the inside to block water draining to the
interior, and to lap the flashing over the pan so water draining
from higher up will be caught by the sill pan (Figure 3).

Figure 2. Flashing Under Brick
Veneer

Step 1:

Install flashing tape over the RO
sill. Let approximately 2 to 3 inches of the flashing lap over the
brick sill. Then, using a taping knife, push the flashing down
between the brick and the existing WRB.
Step 2:

Install a mechanical sill
pan over the flashing tape. The author prefers a metal pan —
copper or (better yet) lead-coated copper. Even vinyl will suffice,
as long as it will keep the water flowing to the outside. This pan
should have a turned-up edge on the inside to create a dam to
prevent water flowing inside and a turned-down edge on the
outside.
Step 3:

Cover the side jambs of
the RO with two strips of flashing tape. To do this, the author
first slits the paper on the back-side cut about 2 inches from one
edge, then peels off the backer on the wide side, using the exposed
tape to cover the RO jambs. This leaves the 2-inch section to stand
straight out of the opening. The author then peels off the
remaining backer paper and uses a taping knife to push the tape
back behind the brick, where it can adhere to the WRB.
Step 4:Here is the tricky part.
Fabricate a top flashing that will slip behind the existing WRB,
and go over the top of the new window, allowing for any trim that
may be installed. Using a taping knife, carefully work the WRB away
from the sheathing. The goal is to separate it from any fasteners
without tearing it up. Once this is done, slip the flashing between
the WRB and the sheathing. You may need to use some flashing tape
to hold this in place.

Figure 3. The author uses a metal brake to
form a copper pan (left). All windows eventually leak, but the pan
will capture the water and allow it to drain to the exterior. The
inside of the pan should have an upturned edge to prevent the water
from draining to the interior, and the side flashings should lap
over the ends of the pan (above).

In some cases, however, there is not enough of a space behind the
brick to push the flashing tape back there. Or, the mortar that
squeezed out on the back side of the brick has clogged the space.
This squeeze out may be chipped away at the edges, but if it's
really heavy, even that won't be enough to provide clearance for
flexible tape. In this case, I bend four aluminum or copper
L-shaped strips, as shown in Figure 4. At a minimum, the legs of
these L-strips should be 2 inches, but a 3- to 4-inch leg is
preferable. Remember: The farther the water is deflected by the
flashing from the edge of the BO, where the most water is likely to
get blown in, the less likely the water will find its way back into
the RO as it drains down the wall.

Figure 4. Alternative Side Flashing
If flexible flashing can't be pushed behind the brick at the sides
of the window opening, the author bends four copper or aluminum
L-strips to use as side flashing instead. To install these, he
starts with the bottom piece, which is as long as at least half of
the height of the window and has a flap that allows the end to
slide down below the sill height. The second piece extends to the
head, with a flap that reaches about 2 inches above the window
opening and is long enough to lap over the first piece
installed.

Installing the Window

Once the sides and the sill have been wrapped, it's time to install
the window. If the BO is tight, we may need to trim back the window
flanges. I often have to completely remove the bottom flange to get
the window in, as well. A jigsaw works for trimming off a formed
vinyl flange. On some windows, it's possible to pull the flange
extrusion out of the frame, or it may require careful trimming with
snips and a utility knife.

Building Science Basics

The goal in any window installation is to keep the outside
environment where it belongs: outside.

The goal in any window installation is to keep the outside
environment where it belongs: outside. By "outdoor environment" we
mean several things: the outdoor moisture, the outdoor air, and the
outdoor temperature. Moisture is the obvious element. Anyone who's
been in the trade knows that all windows will leak eventually. For
this reason, every window should have a sill pan that will catch
water that leaks through the window unit itself, providing drainage
to the outside. The flashing at the head and the sides is meant to
deflect water that leaks past the siding and around the window
trim, shedding it to the outside. Therefore, the order in which the
flashing is installed is important, so lower courses will lap under
the courses above. In a coastal environment where water is likely
to be driven by the wind, it's especially important to use a
self-healing butyl-based adhesive that will seal around the trim
fasteners that will get driven through it. DuPont StraightFlash
(www.dupont.com/construction), Grace Vycor
(www.na.graceconstruction.com), and Pactiv GreenGuard
(www.pactiv.com) are all butyl-based products.

Some contractors try to air seal windows by stuffing fiberglass
in the crack, but this won't work. Fiberglass doesn't stop air
movement. A low-expanding foam sealant will.

Air sealing is less obvious to some builders but not less important
to the performance and durability of a home. The gap around every
window and door in a house represents a serious hole in the
building enclosure, which not only will siphon off conditioned air
from inside the home and pull outdoor air inside where it will
displace conditioned air, but it can also carry moisture vapor that
will condense on the first cold surface it encounters, leading to
mold and rot. The greater the temperature difference between
indoors and out, the more likely this will occur.

The exterior is not the place to deal with air leakage, however.
Instead, seal the window from the interior with a low-expansion,
closed-cell polyurethane foam sealant, such as Great Stuff Pro
Window & Door (www.greatstuff.dow.com), Pur Fill 1G
(www.todol.com), or Touch n' Seal Window & Door Sealant
(www.touch-n-seal.com).

If you get the flashing and air sealing right, then all the
high-performance features of a good window, such as low-E glass and
gas-fills and nonconductive spacers, will be meaningful, and the
chances of the home being able to keep the outside temperature
outside are much greater. — M.S.

When installing the window, first apply caulking to the top and two
side flanges. Without a bottom flange, we don't need caulk there.
But even when we have an intact nailing flange, we never caulk the
bottom of a window. If water leaks through the windows, it must be
able to drain out.

Shim and square the window, and check it for proper operation. In
coastal zones, impact-resistant units usually must be installed
with framing clips, as shown in Figure 5. This actually simplifies
the installation, since the nailing flanges may be hard to get to,
especially at the top. If the window manufacturer does not offer
special metal clips for this purpose, I use a 20-gauge metal tie
plate, such as a Simpson Strong-Tie TP15 or TP35, screwed to the
window first and then folded over at the inside edge of the stud.
If you're unsure what the local codes require in high-wind zones,
it's prudent to check with the code inspector first to make sure
this will work.

Figure 5. Framing Clips for Coastal
Windows
In coastal wind zones, impact-resistant units must be installed
with metal framing clips. These clips also help when the brick
opening is tight and the nailing flange is hard to
access.

After the window is in place, I foam the gap between the window and
the RO with a low-expanding foam to create an effective air seal
(see "Building Science Basics").

Final Flash

With the window installed, I go back outside and apply flashing
tape over the flange. This can be difficult if the BO is tight. If
possible, I push the tape behind the brick. However, if there is
not enough room to get this final flashing behind the brick, I'll
leave it long, allowing it to flap alongside the brick (Figure 6).
Then, after I install the brick mold (or other trim to fill out the
masonry opening), I will trim this excess away and caulk the trim
to the masonry at the sides and bottom of the BO. Across the head,
though, I leave gaps in the caulk to allow any water that might get
past the brick above to escape. Most brick veneer should also have
weep holes above the lintel for exactly this purpose.

Figure 6. The last but often most difficult
step is flashing over the window flanges before the brick mold goes
on. If there's not enough room to slip this flashing behind, the
author will lap the flashing tape onto the brick, and trim off the
excess once the trim is installed.

Mike Sloggatt has been remodeling old homes on Long Island for
more than 27 years and is a member of the JLC Live construction
demonstration team. Photos by the author and his crew.
Illustrations by Chuck Lockhart.